Those screenies are saved in .tga file format, in the RTW folder labelled 'TGA'.

If you have an image-processing program (like PaintShop Pro or Photoshop) switching file formats is a snap. If you don't have such a program, we have TGA viewers available in our files section (courtesy Mizu Clan server)
http://www.mizus.com/Files/k0rgs8gVt/Tools.shtml